The invention relates to method and nozzle for supplying paste fuel to a fluidized bed.
More particularly, the invention relates to a method in comminuting paste fuel which is supplied from a nozzle to a fluidized bed, wherein the fuel in the nozzle is being pressed against an end surface tapering towards the nozzle outlet, and is distributed by means of a jet of splitting air ejected from the nozzle centrally of the fuel flow upstream of the nozzle outlet. EP-A-0182545 discloses a slurry atomizer operating in this way.
In order to secure a satisfactory combustion in furnaces with fluidized bed the paste fuel is dispersed in this way in the combustion chamber as coarse droplets. This dispersion is achieved by means of the jet of splitting air which is called the primary splitting air jet and is directed towards a ceramic cone which forms said tapering end surface. The primary splitting air jet is supplemented by a secondary splitting air jet which is supplied from an annular slot around the nozzle outlet. Experience has shown that there may arise problems by the annular slot being partly clogged, which causes a non-uniformly distributed flow of secondary splitting air and trickle of fuel caused thereby as well as erosion of that part of the nozzle which defines the annular slot, due to generation of vortexes in front of the nozzle. Furthermore, the cooling of the ceramic cone will be unsatisfactory or uneven, which contributes to formation of thermal tension in the ceramic cone and cracks, caused by such tension. If the ceramic cone is replaced by a cone of softer material such as metal the cone will, however, rapidly be destroyed by erosion.
Trickle of the fuel causes formation of agglomerates which fall to the bottom of the combustion chamber and will be sintered there. In prior art nozzles, the distribution of the droplet size is moreover rather wide and the formation of droplets is disturbed by said clogging of the annular slot for secondary splitting air. The nozzles used today are sensitive as far as the strength is concerned and cannot stand today's demand of low flow of splitting air.